Rate's of meteorite impacts on Mars.
This page gives the estimated impact rate on Earth in Fig. 2:
Quantification of Near-Earth Object Threat
http://www.lsst.org/Science/neoquant.shtml
Since Mars is closer to the asteroid belt the impacts rates would be expected to be greater. This figure shows meteorites of size 3 meters and less hit Earth at monthly and greater frequency. The Mars rate would be expected to be higher.
Bob Clark